// 通過類名獲取類
Class catClass = objc_getClass("Cat"); 
 
//注意Class實際上也是對象，所以同樣能夠接受消息，向Class發(fā)送alloc消息
Cat *cat = objc_msgSend(catClass, @selector(alloc)); 
 
//發(fā)送init消息給Cat實例cat
cat = objc_msgSend(cat, @selector(init)); 
 
//發(fā)送eat消息給cat，即調(diào)用eat方法
objc_msgSend(cat, @selector(eat));
 
//匯總消息傳遞過程
objc_msgSend(objc_msgSend(objc_msgSend(objc_getClass("Cat"), sel_registerName("alloc")), sel_registerName("init")), sel_registerName("eat"));

//Cat.m

+ (void)load{
 Method eatMethod = class_getInstanceMethod(self, @selector(eat));
  Method shirtMethod = class_getInstanceMethod(self, @selector(shirt));
 
 method_exchangeImplementations(eatMethod, shirtMethod);
}

- (void)eat{
 NSLog(@"cat eat....");
}

- (void)shirt{
 NSLog(@"cat shirt....");
}

// Cat.m

//An Objective-C method is simply a C function that take at least two arguments—self and _cmd. 
void run(id self, SEL _cmd, NSNumber *number){
 NSLog(@"run for %@", number);
}

//收到run:消息時候，為該類添加一個方法實現(xiàn)
+ (BOOL)resolveInstanceMethod:(SEL)sel{
 if(sel == NSSelectorFromString(@"run:")){
  class_addMethod(self, @selector(run:), run, "v@:@");
  return YES;
 }
 return [super resolveInstanceMethod:sel];
}

//另外針對類方法的為 resolveClassMethod

// 第一步，消息接收者沒有找到對應的方法時候，會先調(diào)用此方法，可在此方法實現(xiàn)中動態(tài)添加新的方法
// 返回YES表示相應selector的實現(xiàn)已經(jīng)被找到，或者添加新方法到了類中，否則返回NO
+ (BOOL)resolveInstanceMethod:(SEL)sel {
 return YES;
}

// 第二步， 如果第一步的返回NO或者直接返回了YES而沒有添加方法，該方法被調(diào)用
// 在這個方法中，我們可以指定一個可以返回一個可以響應該方法的對象， 注意如果返回self就會死循環(huán)
- (id)forwardingTargetForSelector:(SEL)aSelector {
 return nil;
}


// 第三步， 如果forwardingTargetForSelector:返回了nil，則該方法會被調(diào)用，系統(tǒng)會詢問我們要一個合法的『類型編碼(Type Encoding)』
// 若返回 nil，則不會進入下一步，而是無法處理消息
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
 return [NSMethodSignature signatureWithObjCTypes:"v@:"];
}

// 當實現(xiàn)了此方法后，-doesNotRecognizeSelector: 將不會被調(diào)用
// 在這里進行消息轉(zhuǎn)發(fā)
- (void)forwardInvocation:(NSInvocation *)anInvocation {
 // 在這里可以改變方法選擇器
 [anInvocation setSelector:@selector(unknown)];
 // 改變方法選擇器后，需要指定消息的接收者
 [anInvocation invokeWithTarget:self];
}

- (void)unknown {
 NSLog(@"unkown method.......");
}

// 如果沒有實現(xiàn)消息轉(zhuǎn)發(fā) forwardInvocation 則調(diào)用此方法
- (void)doesNotRecognizeSelector:(SEL)aSelector {
 NSLog(@"unresolved method ：%@", NSStringFromSelector(aSelector));
}

//<objc/runtime.h>

struct objc_class {
 Class isa OBJC_ISA_AVAILABILITY;

#if !__OBJC2__
 Class super_class          OBJC2_UNAVAILABLE;
 const char *name           OBJC2_UNAVAILABLE;
 long version            OBJC2_UNAVAILABLE;
 long info            OBJC2_UNAVAILABLE;
 long instance_size          OBJC2_UNAVAILABLE;
 struct objc_ivar_list *ivars        OBJC2_UNAVAILABLE;
 struct objc_method_list **methodLists     OBJC2_UNAVAILABLE;
 struct objc_cache *cache         OBJC2_UNAVAILABLE;
 struct objc_protocol_list *protocols      OBJC2_UNAVAILABLE;
#endif

} OBJC2_UNAVAILABLE;

//Cat+Extend.h

@interface Cat (extend)

@property(nonatomic, copy) NSString *name;

@end


//Cat+Extend.m

@implementation Cat (extend)

- (void)setName:(NSString *)name{
 objc_setAssociatedObject(self, "name", name, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (NSString *)name{
 return objc_getAssociatedObject(self, "name");
}

@end

//<objc/runtime.h>

struct objc_class {
 Class isa OBJC_ISA_AVAILABILITY;

#if !__OBJC2__
 Class super_class          OBJC2_UNAVAILABLE;
 const char *name           OBJC2_UNAVAILABLE;
 long version            OBJC2_UNAVAILABLE;
 long info            OBJC2_UNAVAILABLE;
 long instance_size          OBJC2_UNAVAILABLE;
 struct objc_ivar_list *ivars        OBJC2_UNAVAILABLE;
 struct objc_method_list **methodLists     OBJC2_UNAVAILABLE;
 struct objc_cache *cache         OBJC2_UNAVAILABLE;
 struct objc_protocol_list *protocols      OBJC2_UNAVAILABLE;
#endif

} OBJC2_UNAVAILABLE;

//Cat.h

@property(nonatomic, copy) NSString *cid;

@property(nonatomic, copy) NSString *age;

+ (instancetype)modelWithDict:(NSDictionary *)dict;


//Cat.m

+ (instancetype)modelWithDict:(NSDictionary *)dict{
 id model = [[self alloc] init];
 unsigned int count = 0;
 
 Ivar *ivars = class_copyIvarList(self, &count);
 for (int i = 0 ; i < count; i++) {
  Ivar ivar = ivars[i];
  
  NSString *ivarName = [NSString stringWithUTF8String:ivar_getName(ivar)];
  
  //這里注意，拿到的成員變量名為_cid,_age
  ivarName = [ivarName substringFromIndex:1];
  id value = dict[ivarName];
  
  [model setValue:value forKeyPath:ivarName];
 }
 
 return model;
}